The present invention relates to integrated circuit (IC) packages, and more particularly to a flip chip IC package having an extruded heatspreader that offers more surface area for heat dissipation, as well as a flat surface for an external heatsink attachment, and hence provides the flip chip IC package with enhanced thermal dissipation characteristics.
In the last few decades, the electronics industry has literally transformed. the world. Electronic products are used by, or affect the daily lives of, a large segment of the world's population. For example, telephones, television, radios, Personal Computers (PCs), laptop PCs, palmtop PCs, PCs with built-in portable phones, cellular phones, wireless phones, pagers, modems, and video camcorders, are just a few of the electronic products that have been developed in recent years and which have been made smaller and more compact, while providing more and/or enhanced functions than ever before. The integrated circuit (IC) chip, and the more efficient packaging of the IC chip, have played a key role in the success of these products.
In just the last couple of years, application-specific integrated circuit (ASIC) technology has evolved at a rapid pace. Advantageously, higher clock rates, higher gate counts, cell-based designs and better design tools have converged to enable the creation of complete, high-performance systems on a single IC chip.
The evolution of ASIC technology has mandated new requirements and challenges for IC packaging technology. That is, increasing clock rates make package electrical characteristics more significant in the determination of system performance. Higher gate counts enable the creation of high power, core-limited designs that usually require better and more efficient thermally-enhanced packages. Lastly, increasing system input-output (I/O) requirements mandate packages that support higher lead counts and provide better board assembly yields.
One of the IC packaging approaches that has recently evolved to help meet the challenges of ASIC technology is the IC flip chip package. A sectional view of a conventional IC flip chip package is shown in FIG. 1A. As seen in FIG. 1A, an IC flip chip package 10 typically includes a substrate 16 having an upper surface 11a and a lower surface 11b. An IC die 18 is bonded in or near the center of the upper surface 11a. The IC die, as is known in the art, is formed and cut from a silicon wafer which has been processed so as to include desired electronic circuit components, e.g., transistors, diodes, signal traces interconnecting the transistors, etc. An array of bonding pads is also formed within the die, typically around the periphery of the die, to provide a way to make electrical contact with the electrical circuitry formed in the die.
In many IC packages (not flip chip packages), wire bonds are used to connect each of the IC die bonding pads to a corresponding trace, lead, or pin on a substrate or chip carrier. However, a characterizing feature of a flip chip package is that the die 18 is "flipped over" from its usual IC-die-bonding-pads-up position (to facilitate attachment of a wire bond) to an IC-die-bonding-pads-down position so that the IC die bonding pads face towards the upper surface of the substrate 16. Solder bumps 20 are attached to the I/O pads on the die. Each solder bump 20 is designed to electrically and mechanically bond with a respective solder-bump pad on the upper surface 11a of the package substrate 16. The solder-bump pads, in turn, are then connected through a network of signal traces and vias located on and within the substrate 16 to a corresponding array of solder balls 22 located on the lower surface 11b of the substrate 16. The solder balls 22 may then be soldered to corresponding array of landing pads (not shown) on a printed wiring board (PWB) when the IC package 10 is mounted on the PWB, which PWB forms part of a desired electronic system.
As needed, a metal stiffener 14 may be attached to the upper surface 11a of the package substrate 16. A heatspreader 12 may also be attached to the stiffener 14 by use of an adhesive 28. An advantage of using a flip chip package, such as the package 10 shown in FIG. 1A, is that the flipped-over upper surface is flat and has no circuitry components thereon, thereby providing a good surface to which the heatspreader 12 may be thermally bonded. In addition, flip chip ICs provide more I/O connections than do wire bond ICs due to the use of the full surface area of the IC chip. The heat spreader 12, and stiffener 14, when used, add rigidity to the package and allow heat generated by power consumption within the IC to be dissipated. Removing heat in an IC device is critically important in order to maintain the junction temperature of the various semiconductor junctions used within the IC to within allowable junction temperature limits for reliable operation and long life of the IC. For high power devices, an external heat sink may be attached to the heatspreader 12, as needed.
Still with reference to FIG. 1A, it is common practice, when employing a heatspreader 12, to employ a flat heatspreader that is attached to the package stiffener 14 by a suitable layer of epoxy 28. Unfortunately, the layer of epoxy 28 used to bond the heatspreader 12 to the package stiffener 14 impedes the thermal conduction path to the stiffener.
Disadvantageously, even when dissipated heat is allowed to efficiently reach the heatspreader, only the upper flat surface of the heatspreader 12 is generally exposed or "open" to surrounding ambient air, and thus available for efficiently radiating or convecting heat away from the IC package. (Some heat may also be transferred through the stiffener to the substrate and be dissipated through the substrate to the printed wiring board [PWB] on which the IC package is mounted.) The ability of the heatspreader to dissipate heat thus becomes a function of the available paths for heat dissipation coupled to the heatspreader, and such paths are, in large part, dictated by the open or exposed surface area of the heatspreader in combination with the amount or flow of ambient air that comes in contact with the exposed surface. For high power devices, an external heat sink may be attached to the exposed surface of the heatspreader, thereby effectively increasing the exposed surface area over which heat may be dissipated. For even higher power devices, a blower or fan may be used to further increase the amount of air flow that comes in contact with the exposed surface. But, even external heat sinks and blowers do not allow the lower surface of the heatspreader to efficiently dissipate heat. What is needed, therefore, is a flip chip IC package design that effectively exposes both the upper and lower surfaces of the heatspreader, thereby allowing more heat to be efficiently dissipated through the heatspreader.
Further, because the use of external heat sinks and/or fans or blowers represent additional components that increase the cost of a system employing such components, there is a need in the art for a flip chip IC package design wherein the heatspreader is capable of dissipating more heat than has heretofore been possible, thereby eliminating the need for external heat sinks and/or blowers for all but the very high power applications.